Another all-Minnesota mystery, but this time the stakes are higher. A terrorist cell from Minneapolis has recruited key players and gained access to explosives and the nuclear power plant in Monticello, Minnesota.
The preparation for a Fourth of July celebration is stopped by a tremendous blast in Riverside Park in Mankato. This is first seen as an isolated incidence, but proves to be the first of a pair of explosions that can trigger a nuclear accident that could devastate the Midwest.
Dave, Jim and Willard do what they can to break down the terrorists' plans before they materialize, but will it be enough?